What does a higher entropy value mean?

Higher entropy means the character distribution is closer to uniform and less predictable; a random mix of many different characters scores higher than repetitive text.

What is the maximum possible entropy?

It depends on the alphabet size: the theoretical maximum is log2(N) bits per character, where N is the number of distinct characters used, achieved when every character appears equally often.

Is this the same as password strength?

It's related but not identical; entropy here measures the character distribution of one specific string, while password-strength entropy typically also accounts for the size of the character set an attacker must search.

Text Entropy Calculator Online - Shannon Entropy of Text

Overview

Introduction

Shannon entropy gives a single number for how unpredictable a piece of text is based on its character frequencies, a concept from information theory with practical uses in password strength and compression.

This tool calculates it for you instantly, and it runs entirely client-side, so nothing you paste is ever uploaded to a server.

What Is Text Entropy Calculator?

An entropy calculator that reports the Shannon entropy of your text in bits per character, based purely on how often each character appears.

It runs entirely client-side as part of this site's String Tools collection, so nothing you paste is ever uploaded to a server.

How Text Entropy Calculator Works

Every character in the text is tallied into a frequency map, each character's probability is computed as its count divided by the total length, and the entropy is the negative sum of probability times log base 2 of probability across all characters.

The transformation happens synchronously in JavaScript the moment you type, with no network round trip involved.

When To Use Text Entropy Calculator

Use it to get a rough sense of how random or repetitive a string is, for exploring password strength, comparing generated strings, or estimating how compressible text might be.

It's a fast way to get the answer without opening a stats package, a REPL, or writing a one-off script just to check.

Often used alongside Top Letter Finder, Text Statistics and Random String Generator.

Features

Advantages

Uses code-point-aware character iteration, so multi-byte characters like emoji are counted as single characters.
Reports the unique character count alongside entropy for extra context.

Limitations

Measures only character-level frequency in this one string, not sequence patterns, dictionary words, or true information content in a broader sense.

Examples

Comparing repetitive vs varied text

Input

aaaa

Output

Entropy: 0.0000 bits/character
Unique characters: 1
Total characters: 4

A string made of a single repeated character has zero entropy, since its next character is always fully predictable.

Best Practices & Notes

Best Practices

Compare entropy values only for strings of a similar length and alphabet, since entropy per character is a distribution measure, not an absolute strength score.

Developer Notes

Implemented as `entropy -= probability * Math.log2(probability)` summed over a `Map<string, number>` frequency tally built from `[...input]` (code-point aware iteration, not UTF-16 code units).

Text Entropy Calculator Use Cases

Getting a rough password or passphrase randomness check
Comparing the randomness of generated strings
Estimating how compressible a piece of text might be

Common Mistakes

Treating entropy as a complete password-strength score; it doesn't account for dictionary words, predictable patterns, or the size of the character set an attacker assumes.

Tips

Use the Random String Generator to produce reference strings and compare their entropy against your own text.

Text Entropy Calculator